P475: EMERGING LEUKEMIA ASSOCIATED IMMUNOPHENOTYPES (LAIPS) IN BONE MARROW OF ACUTE MYELOID LEUKEMIA PATIENTS AFTER INTENSIVE CHEMOTHERAPY.
Authors: Lok Lam Ngai, Diana Hanekamp, Angèle Kelder, Willemijn J. Scholten, Jannemieke Carbaat - Ham, Alexander N. Snel, Costa Bachas, Jesse Tettero, Vincent van der Velden, Jennichjen Slomp, Willemijn Hobo, Dimitri Breems, Thomas Fischer, Bjorn Tore Gjertsen, Laimonas Griškevičius, Gunnar Juliusson, Johan Maertens, Markus Manz, Thomas Pabst, Jakob Passweg, Kimmo Porkka, Peter Valk, Patrycja Gradowska, Bob Löwenberg, David de Leeuw, Arjan van de Loosdrecht, Gert Ossenkoppele, Jacqueline Cloos
Journal: HemaSphere (2023)

Background: Measurable residual disease (MRD) is currently implemented to guide consolidation treatment in intermediate-risk AML. Optimization of MRD results is therefore crucial for clinical decision making. MRD can be detected by multiparameter flow cytometry (MFC-MRD) or molecular techniques such as RQ-PCR or next generation sequencing. For MFC-MRD, different approaches are described: 1. The Leukemia-associated immunophenotype (LAIP) approach, where the aberrant phenotypes at diagnosis are monitored during treatment, 2. The Different-from-Normal approach (DfN), where aberrant expression patterns are evaluated without information of the sample at initial diagnosis and 3. a combination of both, which is referred to as LAIP-based-DfN. The advantage of the LAIP approach is knowledge of the diagnostic LAIP for follow up analyses, which enables assessing response to (novel) treatment of the dominant clone. However, a diagnostic sample is needed for this approach and emerging clones due to clonal evolution can be missed. Therefore, the ELN-DAVID AML-MRD guidelines recommend using the LAIP-based-DfN approach. Aims: We investigated the prevalence and the type of LAIPs that are present after 2nd induction cycle (C2), using the LAIP-based-DfN approach in the HOVON-SAKK 132 (HO132) trial. Methods: In samples of de novo AML patients younger than 65 years, we measured all possible LAIPs in the MFC-MRD panel (4 eight-color tubes) published by Cloos et al, 2018 (J. Vis. Exp.) at diagnosis and after second induction cycle (C2) in patients who achieved complete remission (CR/CRi). An emerging LAIP was defined as a LAIP that was absent from the sample at diagnosis. The cut-off of 0.1% (of white blood cells) was used to define MRD positivity. To reduce false negativity, a minimum of 500,000 cells per tube was needed to be measured to call a sample MRD negative when an emerging LAIP was present. When multiple (emerging) LAIPs were present in one sample, the LAIP with the highest percentage was chosen. Results: At diagnosis, 88% (776/884) of the samples contained a LAIP, 11% (94/884) did not contain a LAIP and 2% (14/884) could not be analyzed. After C2, the LAIP approach was used in 77% (476/616) of the samples. The LAIP-based-DfN approach could detect emerging clones in 15% (93/616) of patients. Of these 93 patients, 18% (17/93) had no LAIPs at diagnosis, 2% (2/93) lacked a diagnosis sample and of 78% (73/93), we observed an emerging LAIP next to the LAIP already known at diagnosis. Most frequent emerging LAIPs were CD34+CD56 (31%), CD34+CD22 (16%) and CD34+CD15 (16%). When the MRD positive emerging LAIPs are chosen, the 3 years relapse rates are similar to the relapse rates seen when using the LAIP based approach (Figure 1; LAIP vs LAIP based DfN; CD56 50% vs 57%; CD22 60% vs 50%; CD15 33% vs 44%) Summary/Conclusion: Our data shows that emerging LAIPs can be detected with the LAIP-based-DfN method in follow up and provide similar relapse rates as compared to the LAIP-based method in case a sample at diagnosis is lacking or a LAIP cannot be found. In the HO132 trial only relatively few diagnostic samples were missing. However, in other trials or outside studies that often lack samples at diagnosis, the LAIP-based-DfN approach, can render a substantially increased number of successful MFC-MRD results.Keywords: Minimal residual disease (MRD), Immunophenotype, MDS/AML, MRD